Multiorder diffractive (MOD) lenses are useful for bringing a plurality of spectral components of different wavelengths to a common focus, and are described in U.S. Pat. No. 5,589,982. The MOD lens has a structure of multiple annular zones having step heights defining zone boundaries, which diffract light at different wavelengths into different diffractive orders to a common focus. In contrast, viewing light of multiple different wavelengths through non-MOD diffractive multifocal lens can appear blurry since different wavelengths of light are in focus at different distances. The MOD lenses correct for this problem, but does not provide two different focal distances, e.g., near and distant, useful for providing therapeutic bifocal corrective ophthalmic lenses.
Non-MOD diffractive lenses can have a diffractive profile for diffracting different orders of light at any given wavelength to different focal distances. Such non-MOD multifocal diffractive lenses may be provided on a single lens surface or have zones divided over different surfaces of a lens. Examples of non-MOD multifocal lens are described in U.S. Pat. Nos. 5,017,000; 5,144,483; 3,004,470; 4,340,283; and 4,210,391. Still other non-MOD multifocal lenses have an additional non-MOD diffractive surface correcting for chromatic aberration, as in U.S. Pat. No. 5,117,306.
In order to provide a practical ophthalmic bifocal application utilizing non-MOD multifocal diffractive lens, refractive power can be added to the lens for distance vision correction. Hybrid refractive-diffractive lenses are described, for example, in U.S. Pat. Nos. 5,229,797; 5,104,212; 6,120,148; 5,760,871; and 5,116,111. These hybrid refractive-diffractive lenses are thicker than non-refractive diffractive lenses due to additional lens material needed to add curvature to the lens body. However, thickness reduction is often desirable in ophthalmic applications, such as contact lenses and IOLs. Thus, it would be desirable to provide a diffractive ophthalmic lens for bifocal applications which can utilize diffractive structures without the need to rely on refractive power for distance vision correction.